8.4 - 8.5 - Transcription + Translation

Question 1

What is transcription?

Answer 1

• the process of making pre-mRNA using part of the DNA as a template

Question 2

How is mRNA formed by transcription?

Answer 2

• DNA helicase breaks hydrogen bonds in a section of DNA forming 2 strands, exposing the nucleotide bases
• 1 of the strands acts as a template for free RNA nucleotides in the cytoplasm to join by complementary base pairing
• uracil is used instead of thymine
• RNA polymerase joins adjacent RNA nucleotides together by phosphodiester bonds to form pre-mRNA
• the pre-mRNA is spliced to form mRNA

Question 3

What is splicing?

Answer 3

• when introns are removed and the functional exons are joined together

Question 4

How does mRNA leave the nucleus?

Answer 4

• via a nuclear pore in the nuclear envelope

Question 5

What happens once the mRNA leaves the nucleus?

Answer 5

• it attaches to a ribosome in the cytoplasm

Question 6

How many different tRNAs are there?

Answer 6

• 60

Question 7

How is a polypeptide formed by translation?

Answer 7

• mRNA attaches to a ribosome
• a tRNA molecule, w a specific AA on 1 end + an anticodon on the other, binds to complementary mRNA codon
• another tRNA molecule w a diff. AA binds to the next codon on mRNA molecule
• as ribosome moves along mRNA the AAs join by a peptide bond w use of ATP + an enzyme catalyst to form polypeptide
• 1st tRNA is released after AA joined to polypeptide
• process repeats until ribosome reaches a stop codon

Question 8

How does DNA replication differ from polypeptide synthesis?

Answer 8

• all DNA is copied ( not 1 section - a gene)
• enzyme DNA polymerase involved ( not RNA polymerase)
• takes place in nucleus ( not in nucleus + cytoplasm)
• happens before cell division (not when making proteins)

Question 9

How does the structure of mRNA differ from the structure of pre-mRNA and why?

Answer 9

• pre-mRNA has more nucleotides/introns due to splicing